It might be a problem to explain the right pronunciation because many people from non-Slavic countries simply do not hear the difference between the sounds 's' an 'ś'. I suggest you to use website http://www.ivosoftware.com/ with text-to-speech software to try if you can hear the difference. I have checked that you can obtain quite naturally sounding result if you enter - for example - this text. === Kos, kos, kos. Kosz, kosz, kosz. Koś, koś, koś. ==== kos = blackbird kosz = basket koś = mow, scythe (the imperative). You can practice also with other text. I wish you luck.